Depends on mods, and where you go and when. Northwest of Luzon at the beginning of the Asiatic career there are several invasion task forces, some of them have battleships. Any career you can sneak into Osaka bay and go to Kobe at the north end, there are usually carriers and battleships at anchor there.
This mod;
http://www.subsim.com/radioroom/down...o=file&id=4358
Was designed specifically for that, large numbers of warships to sink.
You really want to get into it I would suggest going into the main folder of SH4, start the Sh4MissionEditor.exe, and just poke around in the \Data\Campaigns\Campaign folder to look at the various career missions.